With the rapid development of high-speed data services, communication capacities and access rates provided by digital subscriber line technologies that transmit signals based on a twisted pair cannot meet requirements of users gradually. Accordingly, a method for extending channels is provided in the industry. By using this method, N−1 extended channels are extended on the basis of N twisted pairs, so that the number of channels including the extended channels reaches 2N−1. In the foregoing method, specifically, extended channels are generated by making a difference between common mode (CM, Common Mode) signals of each two twisted pairs, whereas original channel transmission modes remain unchanged, and signals are still transmitted by using a twisted pair differential mode (DM, Differential Mode). However, signals that are to be transmitted over the extended channels are divided into two equal parts whose directions are opposite to each other, which are transmitted by using the original common mode signals of the two twisted pairs; signals of the extended channels may be acquired at a receiving end by making a difference between the original common mode signals of the two twisted pairs.
To provide a higher access rate for users, multiple twisted pairs are generally bound, and collaborative receiving and sending is performed by using multiple transceivers. In the bound multiple twisted pairs, the extended channel is not unique. Taking binding four twisted pairs Pair 1 to Pair 4 as an example, there may be following three types of extended channels: Type 1. A non-cascade extended channel (NCEC) is extended by making a difference between common mode signals of the Pair 1 and the Pair 4, another NCEC is extended by making a difference between common mode signals of the Pair 2 and the Pair 3, and further, a cascade extended channel (CEC) may be generated by making a difference between common mode signals of these two NCECs; Type 2. An NCEC is extended by making a difference between the common mode signals of the Pair 1 and the Pair 2, another NCEC is extended by making a difference between the common mode signals of the Pair 3 and the Pair 4, and further, a CEC may also be generated by making a difference between the common mode signals of these two NCECs; Type 3. An NCEC is extended by making a difference between the common mode signals of the Pair 1 and the Pair 3, and another NCEC is extended by making a difference between the common mode signals of the Pair 2 and the Pair 4, and further, a CEC may also be generated by making a difference between the common mode signals of these two NCECs. In actual applications, different extended channels are generally selected according to actual requirements. In this way, different extended channels need to be implemented by using a method to meet actual requirements. The prior art provides a solution that different extended channels are implemented by using electronic switches. As shown in FIG. 1, the solution is as follows: When an electronic switch K1 is connected to a circuit 1, an NCEC 1 is extended by making a difference between common mode signals of a Pair 1 and a Pair 2; when an electronic switch K2 is connected to a circuit 2 and an electronic switch K3 is connected to a circuit 3, an NCEC 2 is extended by making a difference between common mode signals of a Pair 3 and a Pair 4; when the electronic switch K1 is connected to the circuit 2, the NCEC 1 is extended by making a difference between common mode signals of the Pair 1 and the Pair 3; when the electronic switch K2 is connected to the circuit 1 and the electronic switch K3 is connected to a circuit 4, the NCEC 2 is extended by making a difference between common mode signals of the Pair 2 and the Pair 4; when the electronic switch K1 is connected to the circuit 3, the NCEC 1 is extended by making a difference between the common mode signals of the Pair 1 and the Pair 4; when the electronic switch K2 is connected to the circuit 1 and the electronic switch K3 is connected to the circuit 2, the NCEC 2 is extended by making a difference between the common mode signals of the Pair 2 and the Pair 3, where the twisted pairs Pair 1 to Pair 4 are also referred to as differential mode channels DM1 to DM4, and a CEC may also be extended by making a difference between the common mode signals of the NCEC 1 and the NCEC 2.
In the solution illustrated in FIG. 1, three electronic switches are set to implement extended channels. When too many twisted pairs are employed, the number of electronic switches is proportional to the square of the number of twisted pairs in the solution illustrated in FIG. 1, thereby increasing difficulties in implementing extended channels and making the system structure more complex.